The present invention relates to polymers, toner compositions, processes for the preparation of polymers, especially telechelic polymers, and more specifically to free radical polymerization processes which provide telechelic or bifunctionalized polymeric products having narrow polydispersity properties. In embodiments, the present invention relates to the utilization of free radical initiators together with free radical reactive monomer compounds and stable free radical agents, such as those illustrated in U.S. Pat. No. 5,332,912 the disclosure of which is totally incorporated herein by reference, to enable the preparation of bifunctional macromolecules which can be selected for crosslinking and permitting the formation of triblock and multiblock copolymers. More specifically in embodiments the present invention relates to providing novel narrow molecular weight pseudoliving homopolymers and copolymer resins that possess latent reactive sites at both ends thereof and wherein, for example, at elevated temperature the aforementioned resins can be reacted with other polymers having a free radical reactive site causing the modification thereof. This reaction can introduce crosslinking in the other polymer or polymers. The reaction of the bifunctional macromolecules with other monomers enables the formation of multiblock copolymers. The products obtained such as the multiblock copolymers can be selected as dispersants, viscosity modifiers, compatibilizers especially for toners with wax, and as polymers for toner compositions. The products obtained with the processes illustrated herein can in embodiments possess narrow polydispersities, that is, narrow molecular weight distributions as defined by the ratio M.sub.w :M.sub.n, wherein M.sub.w is the weight average molecular weight and M.sub.n is the number average molecular weight.
In other embodiments of the present invention are provided processes for the preparation of bifunctional pseudoliving polymeric compounds or bifunctional compounds derived from the addition of stable free radicals to the product resulting from the free radical addition of at least one monomer to a bifunctional free radical initiator compound; processes for further chemical elaboration and modification of the bifunctional polymer compounds; and processes for the chemical preparation and subsequent elaboration of the bifunctional polymer compounds and derivatives thereof. The polymeric bifunctional compounds of the present invention can be used to prepare, for example, triblock copolymers and multiblock polymer having narrow polydispersity properties and optionally wherein at least one of the blocks is water soluble and subsequently added blocks or segments may be only partially or entirely water insoluble thereby providing a means for preparing surface active or surfactant materials having well defined polydispersity and hydrophobe-lipophobe balance (HLB) properties.
Many known polymerization processes for the synthesis of narrow polydispersity resins, such as anionic, cationic and group transfer polymerization processes, are limited by the need for anhydrous reaction conditions and monomers which do not contain protic or reactive functional groups, for example, hydroxyl (OH), carboxyl (CO.sub.2 H), amino (NH), carbonyl (C.dbd.O), active methylene (--CH--C.dbd.O), and the like. As a consequence, these processes are not considered readily applicable to polymerizations in the presence of water or of water soluble monomers since these monomer materials tend to be hydroscopic and any associated water or reactive functional groups may readily destroy the polymerization initiator component, for example, the hydrolysis or protonation of organolithium reagents, or in other ways, cause the polymerization to fail entirely or to be industrially inefficient.
Conventional free radical polymerization processes that are used to polymerize monomers inherently give broad polydispersity resin products or require that sophisticated processing conditions and materials handling protocols be employed.
The polymer resins produced by processes of the present invention, in embodiments, are essentially monomodal, that is the molecular weight distribution is narrow and indicative of a Poisson character and without significant shoulders or side bands. In embodiments, by repeating the heating step, comprising the combined initiation and polymerization step, there is provided a means for obtaining monomodal mixtures of bifunctional polymer resins that are compositionally the same resin type having characteristics of both narrow polydispersity and known or selectable modality greater than or equal to 1. In embodiments, processes of the present invention provide a means for conducting free radical polymerization processes which provide bifunctional resin products on multi kilogram or larger scales. The aforementioned embodiments may be accomplished in a one or single pot reactor environment. In embodiments, polymeric chain growth proceeds by a pseudoliving mechanism and can provide resins of variable molecular weights from very low to very high, for example, less than about 2,000 up to about 200,000 while maintaining narrow molecular weight distributions or polydispersities. In embodiments, triblock and multiblock copolymers can be synthesized by the aforementioned stable free radical moderated polymerization processes wherein each block formed is well defined in length by the sequentially added and reacted monomer and wherein each additional block that is formed also possesses a narrow molecular weight distribution.
It is generally accepted that known anionic and cationic polymerization processes used for the preparation of narrow polydispersity resins, homopolymers, block and multiblock polymers, are not believed possible in aqueous or protic solvent containing polymerization media, reference the aforementioned number U.S. Pat. No. 5,312,704, issued May 17, 1994. The present invention enables the preparation of bifunctional homopolymeric, copolymeric, terpolymeric, block, triblock, and multiblock copolymers which preparation was heretofore not believed effectively possible using free radical polymerization systems.
Of the known polymerization processes a preferred way to prepare polymers or copolymers having a narrow molecular weight distribution or polydispersity is by anionic processes. The use and availability of resins having narrow polydispersities in industrial applications is limited because anionic polymerization processes must be performed in the absence of atmospheric oxygen and moisture, require difficult to handle and hazardous initiator reagents, and consequently such polymerization processes are generally limited to small batch reactors. In addition, the monomers and solvents that are used must be of high purity and anhydrous thereby rendering the anionic process more expensive than alternatives which do not have these requirements. Thus, anionic polymerization processes are difficult and costly. It is desirable to have free radical polymerization processes that provides block and multiblock resins additionally containing bifunctionality that is derived from the addition of stable free radical compounds to the ends of free radical propagating polymer chains and with narrow molecular weight distributions that overcome the shortcomings and disadvantages of the aforementioned anionic polymerization processes.
Free radical polymerization processes are generally chemically less sensitive than anionic processes to impurities in the monomers, reactive functional groups in the monomer, or solvents typically used and are completely insensitive to water.
Polymerization processes are known in the art which proceed by a free radical mechanism providing resins of broad polydispersities and generally high molecular weights. The present invention relates to polymerization processes that proceeds via a pseudoliving free radical mechanism and provide resins of high, intermediate, or low molecular weights, which molecular weight ranges are conveniently determined and controlled by an operator, and which resins possess narrow polydispersities.
The present invention provides product resins with a thermally latent reactive functional group on both ends of the polymer, and which latent functionality can be selectively used in further reactions to prepare other resins with complex architectures. The present invention, in embodiments, provides for polymerization processes that enable control of resin molecular weight, molecular weight distribution, modality of the products, intra-chain monomer composition, and the like properties.
Free radical polymerization processes are industrially important, and are used for the synthesis of numerous copolymers, for example, deflocculating or dispersant polymers. However, resins prepared by free radical polymerization processes typically have broad polydispersities and high molecular weights. When low molecular weight resins are required, a chain transfer agent is typically added to limit the extent of chain growth by way of premature chain termination events and which agent is, for example, an unpleasant smelling thiol. Polymers prepared by thiol type chain transfer polymerization processes are typically irreversibly terminated at either chain end with a functional group, such as alkyl thiol, which precludes further free radical reactions and therefore limits the utility of the polymer resin products produced therefrom.
Copolymers prepared by conventional free radical polymerization processes inherently have broad molecular weight distributions or polydispersities, generally greater than about four. One reason is that most free radical initiators selected have half lives that are relatively long at the temperatures at which the polymerizations are carried out, for example, from several minutes to many hours, and thus the polymeric chains are not all initiated at the same time and which initiators provide growing chains of various lengths at any time during the polymerization process. Another reason is that the propagating chains in a free radical process can react with each other in processes known as coupling and disproportionation, both of which are chain terminating and polydispersity broadening reactions. In doing so, chains of varying lengths are terminated at different times during the reaction process which results in resins comprised of polymeric chains which vary widely in length from very small to very large and thus have broad polydispersities. In the present invention free radical polymerization processes are enabled for producing narrow molecular weight distributions, wherein all polymer chains are initiated at about the same time and premature chain termination by coupling or disproportionation processes is substantially reduced.
Contemporary environmental issues and pollution concerns are prompting greater use of certain biodegradable polymers, among these are water soluble polymers as described by F. Lo, J. Petchonka, J. Hanly, Chem. Eng. Prog., July, 1993, p. 55-58, the disclosure of which is incorporated by reference herein in its entirety. The present invention provides, in embodiments, processes for preparation of various biodegradable and water soluble polymers.
In other applications, such as water treatment, it is particularly important that polymer products have a narrow molecular weight distribution, that is, low polydispersity. In conventional free radical polymerization processes polydispersity rises rapidly as the high molecular weight fraction of the polymer mixture increases. In many processes designed to produce low molecular weight polymers, high molecular weight fractions are observed because there is insufficient control over chain-chain coupling and branching. These high molecular weight fractions tend to dominate the viscosity characteristics of the polymer product and can detract from polymer performance. Other processes designed to produce low molecular weight polymers result in the formation of excessive amounts of oligomeric products, for example, dimers and trimers, which can also detract from the polymer performance. These oligomeric byproducts do not have as much of an affect on the viscosity characteristics of the polymer mixture. However, the oligomers affect the number average molecular weight such that the average is no longer indicative of the properties of the polymer product.
In addition to chain-chain coupling and branching, processes for producing low molecular weight polymer products tend to have high polydispersities resulting from the methods used to reduce the residual monomer content of the polymer product. Methods of reducing the residual monomer content of the polymer mixture include post polymerization processing which employs additional initiator, extended periods at elevated temperatures, and use of comonomeric scavengers. These methods tend to broaden the molecular weight distribution or polydispersity. Therefore, unless the polymer mixture has a sufficiently low polydispersity to begin with, the above mentioned methods used to reduce residual monomer content will raise polydispersity of the product to an unacceptable level.
In the aforementioned U.S. Pat. No. 5,322,912, there is disclosed free radical polymerization processes for the preparation of a thermoplastic resin or resins comprising: heating from about 100 to about 160.degree. C. a mixture comprised of a free radical initiator, a stable free radical agent, and at least one polymerizable monomer compound to form the thermoplastic resin or resins with a high monomer to polymer conversion and a narrow polydispersity.
The following patents are of interest to the background of the present invention, the disclosures of which are incorporated by reference herein in their entirety:
In U.S. Pat. No. 5,247,023, to Chung et al., issued Sep. 23, 1993, disclosed is a polymer compound having boron atoms located at the ends of polymer chain or in the polymer backbone, wherein the boron containing polymer has a formula consisting of: EQU R.sub.1 R.sub.2 B--(CH.sub.2).sub.n --CH.dbd.CH---[Hydrocarbon Polymer]---CH.dbd.CH--(CH.sub.2).sub.m --BR.sub.1 R.sub.2 EQU {[---[Hydrocarbon Polymer]---CH.dbd.CH--(CH.sub.2).sub.n ].sub.m --BR.sub.3-m ---}.sub.x
or combinations thereof wherein n is an integer range from 0 to 12, m is 2 or 3, R.sub.1 and R.sub.2 are the same or different alkyl or cycloalkyl radicals having from 1 to 10 carbon atoms and R is the alkyl or cycloalkyl radicals having from 1 to 10 carbon atoms. Polymeric hydrocarbons having reactive borane group at chain ends or in the polymer chain are described. These types of polymers can be used as intermediate materials for preparing a broad range of polymers which have functional groups located at both ends of the polymer chain, hereinafter alternatively referred to as telechelic polymers. The process of preparing the borane-containing polymers involves metathesis degradation of the polymer at the double bond location in the back bone and simultaneous functionalization of the broken chain ends by borane monomers. Depending on the nature of the borane monomer, the location of boron atoms can be controlled to be at either the chain ends (telechelic) or in the polymer back bone. The concentration of boron in the resulting polymer is related to the reaction time and the mole ratio between borane monomer and the double bonds in the starting hydrocarbon polymer. In turn, the borane groups are interconvertible to various functional groups, such as OH, NH.sub.2, and halides, under mild reaction conditions. Overall, the chemistry is very general and is applicable to most hydrocarbon polymers. A wide variety of telechelic polymers are obtained.
As indicated in the background of the invention section of the aforementioned '023 patent, living polymers are particularly preferred for the preparation of telechelic polymeric materials, that is polymers with functional groups at both chain ends, because these routes provide well defined polymers with a high degree of functional groups at both ends of the polymer chain. However, this process was heretofore previously very limited because only very few monomers undergo living propagation, that is, the aforementioned monomers do not contain reactive functional groups and are not hydroscopic.
In U.S. Pat. No. 5,247,021, to Fujisawa et al., issued Sep. 23, 1993, is disclosed a process for preparing an isobutylene-type allyl-terminated polymer, the process comprising combining: a) a cationically polymerizable isobutylene-containing monomer; b) an organic compound serving as an initiator and concurrently as a chain transfer agent, the organic compound being represented by the formula CR.sub.1 R.sub.2 R.sub.3 X wherein X is a halogen atom, a RCOO-group (wherein R is a monovalent organic group, the same hereinafter) or a RO-group, R.sub.3 is a polyvalent aromatic ring group or a substituted or unsubstituted polyvalent aliphatic hydrocarbon group, and R.sub.1 and R.sub.2 are the same or different and each represent a hydrogen atom or a substituted or unsubstituted monovalent hydrocarbon group, provided that when R.sub.3 is a polyvalent aliphatic hydrocarbon group, R.sub.1 and R.sub.2 can not be concurrently a hydrogen atom; c) a Lewis acid selected form the group consisting of SnCl.sub.4 and TiCl.sub.4 ; and d) a compound serving as an end capping agent agent, the compound being represented by the formula CH.sub.2 .dbd.CHCH.sub.2 SiR.sub.4 R.sub.5 R.sub.6 wherein R.sub.4, R.sub.5 and R.sub.6 are the same or different, and each represent a monovalent organic group or a monovalent organic group containing 1 to 3 silicon atoms, whereby the cationically polymerizable monomer is polymerized at -40 to 10.degree. C.
U.S. Pat. No. 4,581,429 to Solomon et al., issued Apr. 8, 1986, discloses a free radical polymerization process which controls the growth of polymer chains to produce short chain or oligomeric homopolymers and copolymers including block and graft copolymers. The process employs an initiator having the formula (in part) .dbd.N--O--X, where X is a free radical species capable of polymerizing unsaturated monomers. The molecular weights of the polymer products obtained are generally from about 2,500 to 7,000 having polydispersities generally of about 1.4 to 1.8, at low monomer to polymer conversion. The reactions typically have low conversion rates and use relatively low reaction temperatures, of less than about 100.degree. C., and use multiple stages.
U.S. Pat. No. 5,059,657 to Druliner et al., issued Oct. 22, 1991, discloses a polymerization process for acrylic and maleimide monomers by contacting the monomers with a diazotate, cyanate or hyponitrite, and N-chlorosuccinimide, N-bromosuccinimide or a diazonium salt. The polymer produced can initiate further polymerization, including use in block copolymer formation.
Other references cited in an international search report for the aforementioned U.S. Pat. No. 5,322,912 are: J. Am. Chem. Soc., 1983, 5706-5708; Macromol., 1987, 1473-1488; Macromol., 1991, 6572-6577; U.S. Pat. No. 4,628,019 to Suematsu et al., issued Aug. 10, 1986; U.S. Pat. No. 3,947,078 to Crystal, issued Aug. 10, 1976; and U.S. Pat. No. 3,965,021 to Clemens et al., issued Jun. 22, 1976.
The following references may also of interest: U.S. Pat. Nos. 3,682,875; 3,879,360; 3,954,722; 4,201,848; 4,542,182; 4,581,429; 4,777,230; 5,059,657; 5,173,551; 5,191,008; 5,191,009; 5,194,496; 5,216,096; and 5,247,024.
In free polymerization reaction processes of the prior art, various significant problems exist, for example difficulties in predicting or controlling both the polydispersity and modality of the polymers produced. These polymerization processes produce polymers with high weight average molecular weights (M.sub.w) and low number average molecular weights (M.sub.n) resulting in broad polydispersities or low molecular weight (M.sub.n) and in some instances low conversion. Further, free radical polymerization processes of the prior art are prone to generating excessive quantities of heat since the polymerization reaction is exothermic. As the viscosity of the reaction medium increases dissipation of heat becomes more difficult. This is referred to as the Trommsdorff effect as discussed and illustrated in Principles of Polymerization, G. Odian, 2nd Ed., Wiley-Interscience, N.Y., 1981, page 272. This is particularly the situation for reactions with high concentrations of monomer, for example greater than 30 to 50 percent by weight of monomer, which are conducted in large scale reactors with limited surface area and limited heat dissipation capacity. Moreover, the exothermic nature of free radical polymerization processes is often a limitation that severely restricts the concentration of reactants or the reactor size upon scale up.
Further, gel body formation in conventional free radical polymerization processes may result in a broad molecular weight distributions and/or difficulties encountered during filtering, drying and manipulating the product resin, particularly for highly concentrated reactions.
These and other disadvantages are avoided, or minimized with the free radical polymerization processes of the present invention.
Thus, there remains a need for polymerization processes for the preparation of narrow polydispersity telechelic or end group bifunctionalized polymeric resins by economical and scalable free radical polymerization techniques and which polymers retain many or all of their desirable physical properties, for example, hardness, low gel content, processability, clarity, high gloss durability, and the like, while avoiding the problems of gel formation, exotherms, volume limited and multi-stage reaction systems, purification, low yields, limited selection of the starting monomers, performance properties of the polymer resin products, and the like, associated with prior art free radical polymerization methodologies.
The free radical polymerization processes and the resulting telechelic thermoplastic resin products of the present invention are useful in many applications, for example, as a variety of specialty applications including toner and liquid immersion development ink resins used for electrophotographic imaging processes or where monomodal or mixtures of monomodal narrow molecular weight resins or block copolymers with a narrow molecular weight distribution within each block component are suitable for use, for example, in thermoplastic films and solvent borne coating technologies, and for derivatization or modification of other polymeric materials by, for example, crosslinking or grafting reactions.
There remains a need for an economical free radical polymerization process for the preparation of free radical reactive and thermally labile bifunctional or telechelic thermoplastic resins containing or incorporating stable free radical bifunctional groups and which resins possess narrow polydispersities.
There also remains a need for inexpensive, efficient and environmentally sound ways to produce polymers and in particular specifically functionalized polymers having operator controllable or selectable molecular weight properties, and further, processes which selectively afford a wide variety of different polymer product types with narrow molecular weight distribution properties.
The present invention provides pseudoliving free radical polymerization processes which permit the economic preparation of narrow polydispersity resins with low, intermediate, or high molecular weights. The low molecular weight resins can be prepared without a chain transfer agent or molecular weight modifier which thereby provides several advantages over conventional chain transfer mediated polymerization processes.